Electrodes for use in medical implant devices are advantageously designed to be in close contact with the tissue they are intended to stimulate. Where the tissue to be stimulated has a non-planar (e.g. curved) surface profile, problems can arise in ensuring and maintaining the desired contact between the electrodes and the tissue to be stimulated over an entire area of the electrodes of the implant device. In cases where an electrode array includes only a few electrodes distributed over a very small area, the surface profile of the tissue to be stimulated will usually have little impact on the desired electrical contact. As the number of the electrodes and, therefore, the size of the electrode array increases, however, a curvature in the surface profile of the tissue becomes increasingly significant. The curved surface of the retina is one example of an area of the body which presents particular difficulties in achieving the desired contact between the electrodes of a retinal implant and the surface of the tissue containing the nerve cells to be stimulated.
The application of pressure to an implant device and/or to the electrodes of the implant device in order to achieve and/or maintain intimate contact between the electrodes and the tissue to be stimulated is generally undesirable as this can readily lead to irritation and even inflammation of the tissue. One solution to this problem is to design an electrode array which is highly flexible so that it is able to readily adapt itself to the profile of the underlying tissue surface. Such a high degree of flexibility, however, generally requires a very low material thickness and renders handling of the electrode array and/or of the implant device particularly difficult. A very high degree of flexibility in the electrode array also has the additional disadvantage that the electrodes and the current paths incorporated therein can become more susceptible to damage during handling and/or during implantation.
An alternative proposal involves moulding an electrode array of the implant device to have a predefined curvature corresponding to the surface profile of the tissue to be stimulated. This proposal, however, also has the disadvantage that the manufacture of such an electrode array would be problematic. In particular, either a finished substrate that already supports the electrodes of the electrode array would have to be shaped in a mould, thereby introducing an additional production step and providing further opportunities for the electrodes and current paths of the array to sustain damage, or alternatively, the substrate would have to be moulded before the application of the electrodes. This latter option, however, is not possible using the current production techniques, in which the electrodes are manufactured on a flat wafer.
Consequently, there exists a need for a new and improved electrode array for a medical implant device, and a method of producing same. In particular, it would be desirable to provide an electrode array for a medical implant device which is able to be specifically configured or tailored to suit a particular surface profile of the tissue to be stimulated.